1. Field of the Invention
The present invention relates to a semiconductor pressure sensor and a method of producing the same, and more particularly relates to a semiconductor pressure sensor having bridged gauge resistors and a method of producing such a semiconductor pressure sensor.
2. Description of the Background Art
One form of pressure sensors is a semiconductor pressure sensor to which a semiconductor substrate is applied. This semiconductor pressure sensor includes a plurality of diffused resistors to constitute gauge resistors, formed on the surface of a silicon substrate. These diffused resistors are bridged by diffused wiring layers having a low resistance. For example, the gauge resistors are located respectively on the four sides of a predetermined region to constitute a rectangular diaphragm. The silicon substrate has formed on its back surface recesses depressed toward the predetermined region of the front surface. This type of semiconductor pressure sensor is disclosed in, for example, Japanese Patent Laying-Open No. 03-0006824.
However, conventional semiconductor pressure sensors have the following drawbacks. The recesses in the back surface of the silicon substrate depressed toward the predetermined region to constitute a diaphragm are formed by polishing the substrate to a predetermined thickness, and further by etching the back surface of the silicon substrate with a predetermined etching mask interposed.
Accordingly, the diaphragm is controlled in thickness by the etching time, causing the problem in that the diaphragm is likely to vary in thickness in the region to constitute the diaphragm. In addition, even if the diaphragm is to be reduced in thickness, the thickness is restricted to a lower limit of about 10 μm, considering variations in the amount of polishing of the silicon substrate and the amount of etching in the surface of the silicon substrate. There is another problem in that variations in the amount of etching of the silicon substrate cause the recesses to be displaced with respect to the gauge resistors provided for the diaphragm.